Terrestrial Form of Zygnema ( Zygogonium ) ericetorum . 149 
drought) are plainly distinguishable and show that, as a general rule, each 
cell divides at the most but twice between two successive dry periods 
(Fig. 2, H). Apart from the ordinary mode of response to drought, a second 
method of akinete formation has been observed in the early part of the 
year; in this the cells undergo unequal division, resulting in the formation 
of an akinete and of a much smaller pigment-cell (Fig. 2, a). The contents 
of the pigment-cells subsequently disappear, and the empty cells form weak 
points at which rupture of the threads readily occurs. 
Attention is drawn to the extreme adaptation of this form to drought. 
The recovery of the dry filament is practically instantaneous when placed 
in water, there is no marked difference between the osmotic pressure of 
moist threads and those subjected to dryness, and there is no greater 
percentage of dead cells in filaments that have been kept dry for months 
than in those that have been in water for the same length of time. 
Botanical Department, 
East London College, 
November i, 1915. 
Literature cited. 
1. Bohlin, K. (’01) : Etude sur la flore algologique des Afores. Bih. till K. Sv. Vet.-Akad. 
Handl., xxvii, Afd. iii, No. 4, 1901. 
2. Borge, O. (T3) : Zygnemaceae. Die Sussvvasserflora Deutschlands, Oesterreichs 11. d. Schweiz. 
Heft ix, 1913. 
3. Collins, F. S. (’09) : The Green Algae of North America. Tufts College Studies, Scient. 
Ser. ii, 1909. 
4. de Bary (’58) : Unters. iiber die Familie der Conjugaten. Leipzig, 1858. 
5. de Wildeman (’97) : Algues rapportees par M. J. Massart d’un voyage aux Indes Neerlandaises. 
Ann. Jard. Buitenzorg, I er Suppl., 1897. 
6. Fritsch, F. E., and Salisbury, E. J. (T5) : Further Observations on the Heath Association 
on Hindhead Common. New Phytol., vol. xiv, 1915. 
7. Hassall, A. H. (’45): A History of the British Freshwater Algae. London, vol. i, 1845. 
8. Klees, G. (’86) : Ueber d. Organisation d. Gallerte bei einigen Algen u. Flagellaten. Unters. 
d. Bot. Inst. Tubingen, ii, 1886. 
9. Lagerheim, G. (’95) : Ueber das Phycoporphyrin, einen Con jugatenfarbstoff. Videnskab.-Selsk. 
Skrifter, I. Mat.-nat. Kl., 1895, No. 5. 
10. Schmitz (’83) : Die Chromatophoren der Algen. Verh. d. nat. Ver. d. preuss. Rheinl. u. West- 
falens, xl, 1883. 
11. West, G. S., and Starkey, C. B. (’15) : A Contribution to the Cytology and Life-history of 
Zygnema ericetorum (Kuetz.), Hansg., &c. New Phytol., vol. xiv, 1915. 
12. Wille, N. (’90) : Zygnemaceae. In Engler and Prantl, Die natiirl. Pflanzenfam., I. Teil, 2. 
Abt., 1890. 
(’09) : Zygnemaceae. Op. cit., Nachtr. z. I. Teil, 2. Abt., 1909. 
13 . 
